1. Field of the Invention
The present invention relates to a process for coating amorphous ribbon transformer cores and the cores produced thereby. The process utilizes high viscosity bonding material and a support material having a porosity sufficient to allow said bonding material to seep therethrough. The coatings of the present invention impart greater strength to the coated core than previously used coatings, simplify the coating process and minimize the risk of bonding penetration into the core laminations.
2. Description of the Prior Art
Transformer cores are commonly manufactured using silicon steel strips as the magnetic core material. Such cores are rigid, hold their shape and are not very stress sensitive. Alternatively, magnetic cores may be made of amorphous ribbon. While such cores possess improved magnetic properties they are more flexible and require more careful handling during transformer manufacture. Improper handling can lead to ribbon deformation or ribbon sliding and induces mechnical stresses, which results in loss of structural integrity and degradation of magnetic properties. To prevent movement of ribbons and increase rigidity, amorphous ribbon cores have been encapsulated or edge coated.
U.S. Pat. No. 4,789,849 discloses distributed joint amorphous metal transformer cores having lateral edges which are coated with an adhesive bonding agent. No support material is disclosed.
U.S. Pat. No. 4,648,929 discloses a method for producing magnetic cores coated with the composite conformal coating which includes foraminous or porous material, and at least one coat of a UV curable resin. The resin has a low viscosity and the porous material is selected to prevent the resin from passing through the porous material in an effort to prevent penetration between the laminations, which results in degradation of the magnetic properties of the coated core.
U.S. Pat. No. 4,707,678 discloses magnetic cores having a composite conformal coating including a low stress insulative layer having a foraminous insulative sheet impregnated with a first gelled resin bonded to the core edges and bonded to the low stress layer, a high strength structure having at least one insulative layer impregnated with a second resin having higher tensile strength than the first gelled resin. As with the '929 patent, the resin has a low viscosity and the foraminous insulative sheet is selected to prevent the resin from passing through the porous material in an effort to prevent penetration between the laminations.
The UV curable resins of the prior art are low viscosity materials which shrink in volume when cured, causing mechanically induced stresses in the laminations which result in degradation of the magnetic properties of the core. Thus, careful coating and immediate curing are required. Moreover, the foraminous or porous sheets must be very densely woven (cloth-like) to prevent wicking and consequently reduce the range of materials which may be used. The materials of the prior art tend to be fabric-like and would prevent the high viscosity bonding materials of the present invention from wicking through to the core edge.